Many electronic devices permit users to input and manipulate data via the same display screen used to view output from the electronic device. This type of screen is commonly known as a touch screen because it is configured to detect the presence and location of a touch within the display area, such as a touch from a user's finger or from the tip of a stylus or pen. In one example, a touch screen may include resistive digitizer technology, which senses the position of a force that is applied to the surface of screen. Resistive touch screens can detect a fingertip as well as a stylus or pen. In another example, a touch screen may include capacitive digitizer technology, which senses the position of a distortion of the screen's electrostatic field, which results from a conductor, such as a fingertip, contacting the surface of the screen. Unlike resistive touch screens, capacitive touch screens cannot be used through most types of electrically insulating material, such as gloves. A capacitive touch screen may be used with a stylus, provided that it is a stylus having suitable conductive properties.
The term “touch screen” is also commonly used to refer to types of screens that do not necessarily require touch to operate. Such screens may employ active digitizer technology, which is able to detect a signal transmitted by a special type of stylus or pen, such as a pen that transmits a radiofrequency (RF) signal, an ultrasonic signal, an electromagnetic signal, or an infrared signal. For example, touch screen employing active digitizer technology may be configured to detect the presence and position of a signal-transmitting pen that is hovering above the surface of the touch screen, but not actually in physical contact with the touch screen.
This type of signal-transmitting pen, also known as an active pen, requires a power supply for generating and transmitting a signal that is detectable by the associated touch screen. In one example, an active pen may receive power directly, via a tethered cable, from the electronic device that comprises the touch screen. However, a tether between the active pen and the electronic device may be ergonomically inhibitive for the user, and may prevent use of the active pen with other touch screens.
In another example, an active pen may receive power from one or more internal batteries. These batteries will either need to be replaced or recharged from time to time.